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31.
Olga Viedma 《Landscape Ecology》2008,23(6):657-672
Mediterranean landscapes are dynamic systems that undergo temporal changes in composition and structure in response to disturbances,
such as fire. Neither landscape patterns nor driving factors that affect them are evenly distributed in space. Accordingly,
disturbances and biophysical factors interact in space through time. The aim of this paper is to assess the relative influence
of topography and fire on the landscape patterns of a large forested area located in Sierra de Gredos (Central Spain) through
time. A series of Landsat MSS images from 1975 to 1990, and a digital elevation model (DEM) were used to map fires, assess
topographical complexity and evaluate changes in landscape composition and structure. Functional regions across the entire
landscape were identified using different classification criteria (i.e., percentage burned area and topographic properties)
to model topographic and fire impacts at regional scales. A canonical variance partition method, with a time series split-plot
design, quantified the relative influence and co-variation of topography and fire on land cover patterns through time. Main
results indicated that analyzing portions of the landscape under similar environmental conditions and fire histories, the
effects of different fire regimes on the spatio-temporal dynamics of main land covers can be highlighted. However, the impact
of fire on landscape patterns was high variable among regions due to the different regeneration abilities of main land covers,
the topographic constraints and the fire histories of each region. Hence, broad patterns of fire related variance and co-variation
with topography emerged across the entire area due to the different conditions of each landscape portion in which this large
Mediterranean landscape was divided.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
32.
Predicting land cover changes and their impact on the sediment influx in the Lake Balaton catchment 总被引:2,自引:0,他引:2
The land cover pattern in the Lake Balaton catchment (Hungary) has been changing since decollectivization in the 1990s. These
land cover changes significantly impact the landscape connectivity, controlling the influx of sediments into the lake. A comparison
of high resolution land cover maps from 1981, 2000 and 2005 showed a significant extensification of the agriculture with land
cover conversions from arable land and vineyards to grassland and forest. For each land unit transition probabilities were
assessed using logistic regression techniques to evaluate to which extent land cover changes are controlled by physical or
socio-economic parameters. A stochastic land cover allocation algorithm was applied to generate future land cover patterns.
The landscape connectivity for each of the simulated land cover patterns was assessed by means of a distributed routing algorithm.
The simulations suggest that further land abandonment in the upslope parts of the catchment will cause a non-linear reduction
of average soil erosion rates. The changes, however, have a relatively low impact on the sediment volume entering the lake
because of the land unit’s poor connectivity with permanent river channels. The major contributors to the lakes sediment load
are the vineyards near the lakeshore. They are likely to be maintained because of their touristic value. A significant reduction
of the total sediment input in the lake can be expected only if soil conservation measures in the vineyards near the shorelines
are undertaken. 相似文献
33.
Chris S. Duvall 《Landscape Ecology》2008,23(6):699-716
Customary land-use practices create distinctive cultural landscapes, including landscapes where abandoned settlements host
vegetation that attracts wild animals. Understanding how landscape patterns relate to land-use history can help clarify the
ecological effects of particular land uses. This study examines relationships between chimpanzee habitat selection and Maninka
settlement practice, to determine how settlement history has affected chimpanzee habitat in Mali’s Bafing Biosphere Reserve,
where conservation practitioners assume that the characteristic settlement pattern reflects a process of settlement expansion
into undisturbed habitat. Three types of data are reported: (1) ethnographic interviews on settlement history and practice;
(2) systematic sampling of chimpanzee habitat use; and (3) ground-based mapping of settlement sites, surface water, and fruit-tree
patches. These data show that the Maninka have a shifting settlement system, meaning that most sites are occupied for only
relatively brief periods; and that some abandoned settlement sites host fruit-tree patches that are seasonally important chimpanzee
habitat. Two main conclusions are: (1) settlement expansion has not occurred; instead, historic settlement has created habitat
that is both attractive and available to chimpanzees. Anthropogenic habitat does not appear to be vital for chimpanzee survival,
but it spatially and temporally supplements natural habitats. (2) Conservation policies meant to reduce the presumed threat
of settlement expansion may have initiated an unintended, long-term threat of habitat loss for chimpanzees. While settlement
practices may be a component of short-term threats to chimpanzees, such as hunting, when addressing these threats conservation
practitioners should consider long-term settlement processes to avoid creating new threats. 相似文献
34.
35.
David J. Augustine Stephen J. Dinsmore Michael B. Wunder Victoria J. Dreitz Fritz L. Knopf 《Landscape Ecology》2008,23(6):689-697
Sylvatic plague is a major factor influencing the dynamics of black-tailed prairie dog (Cynomys ludovicianus) colonies in the western Great Plains. We studied the nesting response of the mountain plover (Charadrius montanus), a grassland bird that nests on prairie dog colonies, to plague-driven dynamics of prairie dog colonies at three sites in
the western Great Plains. First, we examined plover nest distribution on colonies that were previously affected by plague,
but that had been recovering (expanding) for at least 6 years. Plovers consistently nested in both young (colonized in the
past 1–2 years) and old (colonized for 6 or more years) portions of prairie dog colonies in proportion to their availability.
Second, we examined changes in plover nest frequency at two sites following plague epizootics, and found that mountain plover
nest numbers declined relatively rapidly (≤2 years) on plague-affected colonies. Taken together, our findings indicate that
available plover nesting habitat associated with prairie dog colonies closely tracks the area actively occupied by prairie
dogs each year. Given the presence of plague throughout most of the mountain plover’s breeding range in the western Great
Plains, important factors affecting plover populations likely include landscape features that determine the scale of plague
outbreaks, the distance that plovers move in response to changing breeding habitat conditions, and the availability and quality
of alternate breeding habitat within the landscape. 相似文献
36.
Wind farms are positioned in open landscapes and may cause loss of wildlife habitat due to disturbance, fragmentation, and
infrastructure development. Especially flocking geese, swans, ducks and waders are regarded as vulnerable to wind farm development.
We compared past and current displacement effects of two onshore wind farms and a line of land-based turbines on spring-staging
pink-footed geese (Anser brachyrhynchus) to see if there was evidence of habituation. In one wind farm area, geese previously (1998) (Larsen and Madsen 2000) kept a distance of c. 200 m (the distance at which 50% of peak densities is reached) and they did not go between the turbines;
today (2008) they keep a distance of c. 100 m, but do still not enter the wind farm area. In another wind farm, where foraging
geese previously (2000) kept a distance of more than 100 m and did not enter the wind farm, they now (2008) forage between
the wind turbines and keep a distance of c. 40 m to turbines. In 1998, geese kept a distance of 125 m to a line of turbines,
compared to 50 m now. We conclude that geese have behaviorally adapted to changing landscapes created by wind farms. The difference
in avoidance between the sites may be due to the sizes of the turbines which in this study were small in both rotor-swept
area and in height compared to more recent “industry standard” of 2.5 and 3.0 MW turbines. The study points to the need for
longer term studies to properly assess the impact of wind farms on wildlife, including consequent increased risks from inclement
weather events of feeding, rafting, and migrating waterfowl. 相似文献
37.
Invasions resulting in the transformation of one ecosystem to another are an increasingly widespread phenomenon. While it
is clear that these conversions, particularly between grassland and shrubland systems, have severe consequences, it is often
less clear which factors are associated with these conversions. We resampled plots from the 1930s (Weislander VTMs) to test
whether two widely assumed factors, changes in fire frequency and nitrogen deposition, are associated with the conversion
of coastal sage scrublands to exotic grasslands in southern California. Over the 76-year period, coastal sage scrub cover
declined by 49%, being replaced predominantly by exotic grassland species. Grassland encroachment was positively correlated
with increased fire frequency and, in areas with low fire frequencies, air pollution (percent fossil carbon as indicated by
∂14C, likely correlated with nitrogen deposition). We conclude that increases in fire frequency and air pollution over the last
several decades in southern California may have facilitated the conversion of coastal sage shrubland to exotic grassland systems. 相似文献
38.
Seagrasses, which form critical subtidal habitats for marine organisms worldwide, are fragmented via natural processes but are increasingly being fragmented and degraded by boating, fishing, and coastal development. We constructed an individual-based model to test how habitat fragmentation and loss influenced predator–prey interactions and cohort size for a group of settling juvenile blue crabs (Callinectes sapidus Rathbun) in seagrass landscapes. Using results from field studies suggesting that strong top-down processes influence the relationship between cannibalistic blue crab populations and seagrass landscape structure, we constructed a model in which prey (juvenile blue crabs) are eaten by mesopredators (larger blue crabs) which in turn are eaten by top-level predators (e.g., large fishes). In our model, we varied the following parameters within four increasingly fragmented seagrass landscapes to test for their relative effects on cohort size: juvenile blue crab (prey) predator avoidance response, hunting ability of mesopredators and predators, the presence of a top-level predator, and prey settlement routines. Generally, prey cohort size was maximized in the presence of top-level predators and when mesopredators and predators exhibited random searching behavior vs. directed hunting. Cohort size for stationary (tethered) prey was maximized in fragmented landscapes, which corresponds to results from field experiments, whereas mobile prey able to detect and avoid predators had higher survival in continuous landscapes. Prey settlement patterns had relatively small influences on cohort size. We conclude that the effects of seagrass fragmentation and loss on organisms such as blue crabs will depend heavily on behaviors of prey and predatory organisms and how these behaviors change with landscape structure. 相似文献
39.
Shafarin MS Zamri-Saad M Khairani BS Saharee AA 《Tropical animal health and production》2008,40(5):335-340
This report describes the proliferation and transmission patterns of Pasteurella multocida B:2 among stressful goats, created through dexamethasone injections. Thirty seven clinically healthy adult goats were divided
into three groups consisted of 15 goats in group A, 11 goats in group B and the remaining 11 in group C. At the start of the
study, all goats of group A were exposed intranasally to 1.97 × 1010 CFU/ml of live P. multocida B:2. Dexamethasone was immediately administered intramuscularly for 3 consecutive days at a dosage rate of 1 mg/kg. The exposed
goats were observed for signs of HS for a period of 1 month. At the end of the 1-month period, 11 goats from group B were
introduced into and commingled with the surviving goats of group A before all goats from both groups were immediately injected
intramuscularly with dexamethasone for 3 consecutive days. The treatment with dexamethasone was then carried out at monthly
interval throughout the 3-month study period. Goats of group C were kept separately as negative control. Three surviving goats
from each group were killed at 2-week interval for a complete post-mortem examination. Two (13%) goats of group A were killed
within 24 hours after intranasal exposure to P. multocida B:2 while another two (13%) goats from the same group were killed on day 40, approximately 10 days after the second dexamethasone
injection. All four goats showed signs and lesions typical of haemorrhagic septicaemia. Bacteraemia was detected in 3 goats
of group A that were having rectal temperature higher than 41°C. The P. multocida B:2 isolation pattern was closely associated with dexamethasone injections when significantly (p < 0.05) higher rate of isolations
from both groups were observed after each dexamethasone injection. Transmission of P. multocida B:2 from goats of group A to group B was successful when P. multocida B:2 was isolated from goats of group B for a period of 28 days. There was a strong correlation between dexamethasone injections,
rate of bacterial isolation and serum cortisol level. The IgG level showed an increasing trend 2 weeks after exposure to P. multocida B:2 and remained high throughout the study period. 相似文献
40.